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Name: Don W.
Status: student
Age: 40s
Location: N/A
Country: N/A
Date: Wednesday, June 26, 2002

Why does the mercury light from public lighting appear blue, even though there are yellow and green lines also appearing in the spectrum?

Mercury has a rich atomic line spectrum. The "blue" appearance is due to the fact that the emission line at 435.8 nm is much more intense than other emission lines in the visible region. In the design of mercury lamps the conditions of pressure, and other design parameters are optimized to maximize its output at this wavelength. An analogous situation occurs with "sodium" street lamps that have a characteristic yellow appearance due to the intense sodium emission.

Vince Calder

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